Recently, electric vehicles including hybrid vehicles, electric cars, etc. have become more widespread. Most electric vehicles use a system to drive a motor or a motor generator with alternating current power obtained by converting direct current power of a battery using inverters. Use of a boosting converter (voltage converter) has recently become common to raise a voltage of the battery and supply the raised voltage to the motor. As a result, the rotational speed of the motor is increased and a torque operating range is widened, whereby travelling performance (speed, acceleration/deceleration performance) of the electric vehicle is often improved. Further, a recently used electric vehicle includes a plurality of batteries connected in parallel and mounted on the vehicle to increase the battery capacity, such that the vehicle can travel with the motor alone. Such a vehicle has a longer cruising distance with so-called electricity (EV) travelling. Meanwhile, a power supply system capable of changing on/off operation patterns of four switching elements to switch between serial and parallel connections of batteries, or provide various operating modes, such as boosting the voltage in the serial connection of the batteries or in the parallel connection of the batteries, etc., has also been proposed (e.g., see JP 2012-70514 A).
In the batteries connected to such a power converter as disclosed in PTL 1, the temperature of each battery is not always the same and changes variously according to the operating mode of the power converter. In some of the batteries, therefore, the temperature may become sufficiently high to cause input/output restriction (input/output current restriction). In contrast, the temperature may become sufficiently low to cause the input/output restriction (input/output current restriction). In such a case, required power for the vehicle may not be supplied due to the output restriction of the batteries because of the temperature.
Patent Document 1: JP 2012-70514 A